drm/mediatek: fix unbind functions

detatch panel in mtk_dsi_destroy_conn_enc(), since .bind will try to
attach it again.

Fixes: 2e54c14e ("drm/mediatek: Add DSI sub driver")
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Signed-off-by: CK Hu <ck.hu@mediatek.com>

drivers/gpu/drm/mediatek/mtk_dsi.c

@@ -844,6 +844,8 @@ static void mtk_dsi_destroy_conn_enc(struct mtk_dsi *dsi)
 	/* Skip connector cleanup if creation was delegated to the bridge */
 	if (dsi->conn.dev)
 		drm_connector_cleanup(&dsi->conn);
+	if (dsi->panel)
+		drm_panel_detach(dsi->panel);
 }
 
 static void mtk_dsi_ddp_start(struct mtk_ddp_comp *comp)